I just put the Apex kit into my 640. I'm hoping everyone understands this kit is a dedicated parts replacement made to work together in conjunction with each other. This isn't a put in which parts you feel like kind of kit, nor is it a spring selection that can be changed out for a different one from elsewhere. You add the very carefully selected pair of springs and you replace the firing pin for one that is just slightly longer to insure primer ignition from said springs. I don't have a trigger pull scale but it does feel noticeably easier to pull the trigger while still being heavy enough to not have a feeling of being dangerously light, but that will be subjective to any who try this kit. My only complaint is that the trigger return does have a funny almost mushy feel to it. It's not dragging and it doesn't alter function for the negative. It just doesn't feel as smooth as the trigger pull. I plan on trying various reloads and maybe a few factory options, but I can tell just by observing it in action that it should thwack that primer pretty good and I will be able to better aim while pulling the smoother lighter trigger. So far, I approve.